Ropes of synthetic fibers



.Aug. 25, 1964 R. J. LAURETI ROPES OF SYNTHETIC FIBERS Filed Nov. 231962 F I G. 4.

F l G. 2.

INVENTOR.

REMO J. LAURETI BY a w i/flrz ATTORNEYS United States Patent 3,145,525RGPES 0F SYNTIETIC FIBERS Remo .l. Laureti, Moerestown, N.J., assignorto Wall Rope gvorks, Inc, Beverly, NJ., a corporation of New ersey FiledNov. 23, 1962, Ser. No. 239,420 8 Claims. (Cl. 57-140) This inventionrelates to ropes of synthetic fibers, and particularly to ropes formedto a major extent of polypropylene.

The advantages of rope made of polypropylene are well recognized. Theyare characterized by light weight, chemical inertness so that they areproof against rotting and deterioration due to chemicals normallyencountered in use, they do not absorb water, have little stretch, andhave high tensile strength. However, they have the drawback,particularly for maritime uses, especially towing, that they tend tostick to timber heads and bitts so that when stressed they move in rapidjerks resulting in rapid deterioration. The deterioration has beenascribed to the generation of heat in these rapid jerking movements,polypropylene having -a rather low melting or softening point so thatthe surface fibers are destroyed. Following up this theory, it has beenproposed to form the strands of a largely polypropylene rope with anouter layer of yarns including a substantial number of synthetic yarnsof higher melting point material. Higher melting point yarns selectedfor this purpose have been typified by nylon. Polyester and cellulosefiber yarns have also been proposed, all of these having higher meltingpoints than polypropylene.

But these materials have various disadvantages typified by nylon whichhas been found to be the best. Nylon has a high coefiicient of frictionwith respect to wood or iron, and must be carefully lubricated withspecial lubricants which will not be removed by immersion in water.Nylon is also water-absorbent and shrinks when exposed to water, and itsultimate elongation and tensile strength vary greatly with its moisturecontent. Accordingly, nylon is not compatible with polypropylene yarns.This incompatibility is also true with respect to polyester andpolypropylene yarns.

It is the general object of the present invention to provide rope whichmay be regarded as of the polypropylene type in that, most desirably,its constitution is mainly of polypropylene, which rope hassubstantially all the desirable qualities of polypropylene rope but doesnot have its tendency to stick.

A further object of the invention is to provide a polypropylene type ofrope which requires no lubricant.

In brief, in accordance with the invention, the rope is provided atleast at its exterior with a substantial proportion of polyethylenefibers. Polyethylene is light in weight and less expensive as comparedwith nylon and polyester. But these are not its major advantages overnylon and polyester. One of its advantages is that it may be madecompletely compatible with polypropylene in its elastic properties. Bothpolypropylene and polyethylene may be produced with varying elasticproperties; but the ranges of these are, or can be made, very similar,and for any polypropylene there may be chosen a polyethylene ofsubstantially the same elastic properties. Polyethylene, furthermore,has elastic properties which are independent of exposure to moisture,the same being true of polypropylene.

Its outstanding advantage utilized in accordance with the invention isthat it has a relatively low coeflicient of friction with wood or steel,much less so than either nylon or polyester; and not only in itself butin combination with polypropylene it provides adequate low frictioncharacteristics for a rope. While not as strong as polypropylene, nylonor polyester, it has sufficiently high strength that, when it forms arelatively minor constituent of the complete rope there is littledilference in strength between the composite rope and a purepolypropylene rope.

Through its use, a polypropylene type rope, by which is meant a ropehaving the general characteristics of an all polypropylene rope byreason of a major polypropylene content, may be provided which does nothave the sticky characteristic leading to destruction of the rope asdescribed above. Whereas this problem has been solved in one way by theproposal referred to, i.e., by sheathing polypropylene rope with yarnshaving higher melting point but requiring lubrication to lessen frictionto a satisfactory degree, the same problem is solved in accordance withthe present invention by making use of the lubricating qualities ofpolyethylenes. In the solution in accordance with the invention, addedlubricant is entirely unnecessary. The result, furthermore, is achievedwithout taking into consideration any matter of melting points. In fact,as noted, polyethylenes compatible with polypropylenes have lowermelting points than the polypropylenes. Stated briefly, the troublesencountered by reason of heat generation are overcome by prevention ofthe generation of heat by lowering the effective friction and providingfor smooth sliding between the rope and the bitts or the like aboutwhich it is trained.

As will appear, the effective utilization of polyethylene may beachieved in various fashions, all substantially equally effective, whichprovide a substantial polyethylene content at the exterior of the rope.

The general objects of the invention together with others relating todetails, will be apparent from the following description, read inconjunction with the accompanying drawing in which:

FIGURE 1 is a side elevation of one form of poly propylene type ropeprovided in accordance with the invention;

FIGURE 2 is a transverse section taken on the plane indicated at Z-2 inFIGURE 1, the showing being diagrammatic;

FIGURE 3 is an elevation of diagrammatic type illustrating a ply whichmay be used in forming a rope in another embodiment of the invention;and

FIGURE 4 is a relatively enlarged cross-sectional view showing thecomposition of a yarn which may be used in a further embodiment of theinvention.

Referring first to the modification illustrated in FIG- URES 1 and 2, arope 2 is illustrated as formed of laid strands 4 each formed of pliesgenerally indicated at 6, formed of twisted yarns. From the geometricstandpoint, the rope illustrated is merely typical, the invention notbeing concerned with or limited to the particular arrangement of yarns,plies, or strands. As will be evident to those versed in this art, theinvention is quite universally applicable irrespective of the particulargeometric nature of the rope. However, for purposes of description ofthe invention, a particular rope is illustrated which from the geometricstructural standpoint is conventional. Because of confusion interminology, the makeup of such a rope may be briefly described. Thebasic elements are fibers or filaments, these two terms being usedrather interchangeably, except that fibers is the usual designation whennatural staple fibers of limited length are used, and filaments is moregenerally used in speaking of artificial materials, such as those withwhich we are here concerned, which are drawn into continuous filamentsof indefinite length.

The fibers or filaments are then formed into yarns by twisting, thisterm being equivalently referred to, at times, as threads or singlesyarns. The yarns just referred to are then twisted to form what areknown as plied yarns, ply yarns, or, simply, plies. Another equivalentterm sometimes used is cords, but this term is more aptly used withreference to plied yarns twisted together.

The plied yarns or plies or sometimes cords in the stricter sensereferred to are then formed into strands. While strands contain twisted.plied yarns or cords, they generally have special structure: thecomponent plies or cords are not merely arbitrarily twisted but arearranged in generally concentric layers, so that there is a distinctlayer of plies at the exterior of each strand. The plies of this outerlayer of a strand are of particular interest herein.

The strands are then laid into rope, there being, usually, three strandsin a rope. With the foregoing preliminary discussion, it will now beseen, with particular reference to FIGURE 2, that the plies, generallyreferred to as 6, are associated in the strands in this layer fashion.In the specific arrangement illustrated, it may be considered that theplies of all layers of a strand except the outermost are formed ofpolypropylene. It is the outermost layer of plies which will now beprimarily discussed. The outermost layer is shown as formed ofalternating plies of two sets of different compositions. The plies 8 ofone set are formed of yarns It) of polypropylene. The plies I2 of theother set are formed of yarns 14 of polyethylene.

The rope just described is highly satisfactory in showing no tendency tostick on bitts or other members about which it is trained. This isapparently due to the fact that its surface presents only smallseparated areas of polypropylene to the area with which the rope makescontact and in the direction of lengthwise movement of the rope asslipping occurs. Bounding each small presented area of the polypropyleneis either polyethylene or the interruption of contact occasioned by thecurvature of the strands into the troughs or grooves between them. Itmust, of course, be remembered that in actual use when the rope istrained about an object and under load what would be essentially onlypoint or line contacts (in unloaded condition) are very considerablyfiattened so that area contacts actually exist. the fact that anyelemental area of contact presenting polypropylene to the other surfaceis quite limited and bounded at least in part by surface areas ofpolyethylene which have the low friction aspect previously described,the situation is essentially as if the rope was lubricated.

While in FIGURES 1 and 2 the polypropylene and polyethylene pliesalternate, it is quite satisfactory to lessen the proportionate amountof polyethylene in the exterior layer of a strand by having in thislayer a polyethylene ply as every third ply or every fourth ply, theothers being of polypropylene. The same situation is presented of havingthe polypropylene presented on the surface of the rope in onlyrelatively small separated areas.

The structure may also involve an excess of polyethylene plies overpolypropylene plies in the outer layer of a strand; e.g. there may betwo or more plies of polyethylene per ply of polypropylene, and, in thelimit, all of the plies of the outer layer may be of polyethylene.

With any of the aforementioned constructions it will be noted that themajor cross-section of the rope is polypropylene. Accordingly, the ropeexhibits, so far as flexibility, strength and other characteristics areconcerned, those of an all polypropylene rope. The polyethylene contentis only a relatively minor percentage of the whole and, in itself, hasproperties of strength at least approaching those of polypropylene sothat there is little loss of strength of the rope as compared with oneconsisting only of polypropylene.

The same principles of preventing sticking and of lubrication may beachieved in other fashions. One of these is illustrated in FIGURE 3 inwhich a ply 16 is formed by twisting two yarns 18 of polypropylene withone yarn 20 of polyethylene. Such plies 16 may form all of the plies ofthe outer layer of each strand. Under these Apparentlyconditions thereis again the interruption of continuity of the polypropylene presentedat the surface of the rope, the continuity of the areas of polypropylenebeing broken up by areas of polyethylene. In this arrangement theindividual areas of polypropylene average as greater than in the ropefirst described. The composite plies such as 16 may alternate with pliesof polypropylene in the outer layer of each strand. It will be evidentthat plies may also involve two or more yarns of polyethylene and one ofpolypropylene.

Still another modification may be used as illustrated in FIGURE 4 whichshows a ply 22 in which the individual yarns 24 are made up of filamentsof polypropylene 26 and polyethylene 28 twisted together. In theformation of these yarns actual layering is not achieved, the filamentsbeing arranged essentially at random and twisted together. Theproportion of polyethylenefila ments 28 to polypropylene filaments 26may vary from, for example, about 1:5 to 1:1, or more. As will beimmediately evident, therefore, because of the rather randomdistribution, quite small areas of the two yarns are presented at thesurface of the ply. The plies 22 thus produced may be incorporated inthe strand in the outer layer of plies thereof with the special plies 22of the mixed filaments alternating with plies of polypropylene as in thecase of FIGURE 1, the mixed plies taking the place of theall-polyethylene plies 12. The result of absence of sticking qualitiesand of effective lubrication still results. The mixed plies 22 may formall of the outer layer of each strand.

It will be evident, of course, that the yarn 20 of FIG- URE 3 may be ofthe type shown at 24 in FIGURE 4. Obviously there are other combinationswhich may be used introducing adequate amounts of polyethylene into thesurface layers of the strands.

The proportion of polyethylene to polypropylene in the outermost layerof a strand depends entirely upon the use to be made of the rope. Wherevery heavy loadsare expected to be encountered, the proportion ofpolyethylene to polypropylene may be high, as 1:1 to 1:2. On the otherhand if minor loads are involved orless aspects of rubbing are expected,the proportion of polyethylene to polypropylene presented by the outerlayer of plies of the strand may be less. What is to be avoided,however, is the possibility that large areas of propylene withoutinterruption by polyethylene might be presented at the rope surface.

It will be evident that the invention is applicable to ropes in whichthe polypropylene and/ or the polyethylene filaments may be blended withother filaments, natural or artificial, which may be used in ropeconstruction; nevertheless the protection of the polypropylene filamentsby the polyethylene filaments may be achieved as already described.

In summary, the rope may be said to be formed, at least in part, ofpolypropylene and polyethylene filaments and comprising a plurality ofstrands, each strand being formed of an outer layer of plies andinterior plies, the interior plies being formed primarily ofpolypropylene, and the outer layer of each strand presenting exteriorlyof the rope one or more polypropylene areas interrupted by areas ofpolyethylene and presenting to a curved surface engaged under stressesby the rope areas of both polypropylene and polyethylene. In the case ofthe rope shown in FIGURES 1 and 2, the polypropylene areas of a strandare presented by the individual polypropylene plies which are separatedby polyethylene plies. In the case of a rope formed using the plies ofFIGURE 3, the corresponding areas are provided by the exposed surfacesof the two types of yarns. In this case, assuming plies such as shown at16 alternate with plies formed solely of polypropylene, thepolypropylene presented area is continuous in the sense that in apicture of the rope a line could be continuously drawn through adjacentpolypropylene yarns; but theoverall area is still interrupted at closeintervals by polyethylene, so that a surface engaged by the rope undertension would have both polypropylene and polyethylene areas presentedon it. In the case of the use of yarns of mixed filaments, the areasthus presented are much smaller. The overall aspect is that sufficientpolyethylene is close to any polypropylene region so as to produce thelubricating effect which has been described, preventing the stacking ofthe polypropylene.

Further, as already described, the entire outer layer may consist ofpolyethylene, the interior layers comprising, largely, polypropylene.

It will be obvious from the foregoing that variations may be made indetails of application of the invention without departing therefrom asdefined in the following claims.

What is claimed is:

1. A rope of polypropylene and polyethylene filaments comprising aplurality of strands, each strand being formed of an outer layer ofplies and interior plies, the interior plies being formed primarily ofpolypropylene, and the outer layer of each strand presenting exteriorlyof the rope one or more polypropylene areas interrupted by areas ofpolyethylene and presenting to a curved surface engaged under stress bythe rope areas of both polypropylene and polyethylene.

2. A rope according to claim 1 in which the outer layer of each strandis formed of plies primarily of polypropylene interspersed with pliescontaining polyethylene.

3. A rope according to claim 1 in which the outer layer of each strandis formed of plies primarily of polypropylene interspersed with plies ofpolyethylene.

4. A rope of polypropylene and polyethylene filaments comprising aplurality of strands, each strand being formed of an outer layer ofplies and interior plies, the interior plies being formed primarily ofpolypropylene, and the outer layer of each strand presenting exteriorlyof the rope at least some areas of polyethylene and at least some areasof polypropylene to a curved surface engaged by the rope under stress.

5. A rope comprising a plurality of strands, each strand being formed ofan outer layer of plies and interior plies, said interior plies beingformed primarily of polypropylene, said outer layer of plies containingat least one yarn primarily of polypropylene and at least one yarnprimarily of polyethylene.

6. A rope comprising a plurality of strands, each strand being formed ofan outer layer of plies and interior plies, said interior plies beingformed primarily of polypropylene, said outer layer containing plieshaving at least one yarn of mixed polypropylene and polyethylenefilaments.

7. A rope comprising a plurality of strands, each strand being formed ofan outer layer of plies and interior plies, said interior plies beingformed primarily of polypropylene, all of said plies of said outer layerof each strand containing polyethylene.

8. A rope comprising a plurality of strands, each strand being formed ofan outer layer of plies and interior plies, said interior plies beingformed primarily of polypropylene, all of said plies of said outer layerof each strand being formed of polyethylene.

References Cited in the file of this patent V UNITED STATES PATENTS2,591,628 Snyder Apr. 1, 1952 2,804,745 Foster Sept. 3, 1957 3,026,669Stanton Mar. 27, 1962 3,043,086 Hood July 10, 1962

1. A ROPE OF POLYPROPYLENE AND POLYETHYLENE FILAMENTS COMPRISING APLURALITY OF STRANDS, EACH STRAND BEING FORMED OF AN OUTER LAYER OFPLIES AND INTERIOR PLIES, THE INTERIOR PLIES BEING FORMED PRIMARILY OFPOLYPROPYLENE, AND THE OUTER LAYER OF EACH STRAND PRESENTING EXTERIORLYOF THE ROPE ONE OR MORE POLYPROPYLENE AREAS INTERRUPTED BY AREAS OFPOLYETHYLENE AND PRESENTING TO A CURVED SURFACE ENGAGED UNDER STRESS BYTHE ROPE AREAS OF BOTH POLYPROPYLENE AND POLYTHYLENE.